The prior art is already aware of arrangements for park-lock mechanisms which utilize pawls which are movably mounted for engaging the park gear and thus hold the transmission in a non-operative position. In these prior art arrangements, various adaptations and means are employed for moving the pawl into engaged position with the park gear, and also various arrangements and means are utilized for releasing the pawl from the gear so that the transmission can operate. One prior art park-lock mechanism for transmissions is disclosed in U.S. Pat. No. 3,990,541 where a pawl or latch is pivotly mounted and under the influence of a spring for engagement and disengagement with the gear. Beyond the prior art patents cited in the aforesaid patent, other prior art patents are U.S. Pat. Nos. 2,865,227 and 2,875,856 and 3,074,513 and 3,116,815 and 3,300,001 and 3,856,119. These prior art patents generally show pivotally mounted pawls or latches which move into engagement with the park gear so that the transmission cannot be operated and thus the vehicle is retained in a static or parked position.
One of the concerns with respect to the prior art is that there is significant force between the pawl or latch and the park gear itself, since the engaged teeth are forced against each other. Accordingly, it is difficult to retract the pawl or latch from the park gear teeth, and the force between the teeth must be overcome before the retraction can be accomplished. Of course when the vehicle is parked on an irregular surface or on an incline, such that it tends to roll either forward or backward, then the force between the teeth is considerable and it takes special mechanism and force to release the park gear. Further, since the force exists between the engaged teeth under certain conditions, such as those mentioned, then the elements forming the construction must be sturdy and even complex so that the operator can overcome the gear teeth force and release the park gear when desired. A shift mechanism is commonly employed for releasing the pawl or latch, and that is manually operated and thus the operator must force on the lever in a sufficient amount to effect the release.
Still further, in the prior art arrangements, such as those mentioned above, the force between the latch or pawl teeth and the park gear teeth is such that the teeth are subject to being worn and even broken, and thus the expense, reliability, and need for repair are of concern in the prior art constructions.
The present invention came about upon recognizing the aforemention problems, and the present invention overcomes the aforementioned problems and thus provides a park-lock mechanism which is highly reliable, inexpensive, sturdy for the forces and purposes to which it is subjected, and which is easily manufactured and maintained.
Another and important object of this invention is to provide a park-lock mechanism which accomplishes the aforementioned and which does so with a construction which utilizes the force tending to rotate the park gear for actual release of the latch or pawl itself. That is, once only an initial manual movement is made for releasing the latch or pawl, then the force presented by the park gear itself is utilized for further release of the latch or pawl.
Still further, and still with respect to the aforementioned objectives and advantages, the park-lock mechanism of this invention provides a construction which is not subject to excessive wear and likelihood of damage, such as breaking the gear teeth, and this is accomplished by having the latch or pawl itself released in the direction which the park gear itself tends to rotate, to thus avoid wear and danger of breakage.
Therefore, the objects and advantages of this invention include the arrangement of a park-lock mechanism which has effortless park-lock disengagement regardless of direction of load, or amount of load, due to the inherent load assistance of the design itself. Also, there is positive disengagement of the park-lock pawl from the park gear without having to depend on gear tooth angle and over-designed springs to effect this engagement. Further, there is less wear on the parts because the pawl itself moves out of mesh with the park gear instead of being forced or pulled out of engagement. In fact, the park-lock pawl of this invention and the park gear are moving at the same speed and in the same direction during the disengaging process and they continue to do so until they become fully disengaged, and there is thus no excessive wear and in fact only minimal wear.
Other objects and advantages will become apparent upon reading the following description in light of the accompanying drawings.